Index of content:
Volume 58, Issue 2, August 1975
58(1975); http://dx.doi.org/10.1121/1.380673View Description Hide Description
In connection with a celebration of Professor Walter G. Cady’s approaching 100th birthday, a resume of some of his most important works on piezo and ferroelectric crystals were discussed. This celebration was held at Wesleyan University in Middletown, Connecticut where he was a professor for over 40 years. Briefly he was the inventor of the crystal‐controlled oscillator, the very selective narrow‐band crystal filter, one of the principal theorists of the ferroelectrical effect in crystals, and the historian par excellence of the science of piezoelectric crystals. These initial efforts have led to many applications, such as (1) crystal filters for separating out the many telephone channels that can be transmitted over radio systems, coaxial systems, and undersea cables; (2) crystal‐controlled oscillators and time standards of use for radio broadcasting, navigation systems, and crystal‐controlled watches; (3) ferroelectric crystals and ceramics which are widely used in such applications as ultrasonic cleaners, medical applications, devices for generating high voltages, and particularly in underwater sound transducers.
Subject Classification: 10.60; 85.52.
58(1975); http://dx.doi.org/10.1121/1.380674View Description Hide Description
The transient scattering of spherical pressure pulses by an infinitely long acoustically hard circular cylinder is analyzed. The pressure in the neighborhood of the reflected wavefront is calculated by the method of series expansion in conjunction with the transport equations. From the wave equation, a simple integral formula is derived by means of which the solution to the present three‐dimensional problem can be effectively constructed from the two‐dimensional line source solution. Thus, the pressure in the neighborhood of the diffracted wavefront is computed based upon Friedlander’s diffraction formulas pertaining to the scatttering of a cylindrical pulse by a hard cylinder. Outside the neighborhood of the scattered wavefronts, the solution is obtained by the Fourier series and integral transform techniques and is accurately computed by this formula. By combining the various solutions, the true time histories of the scatteredpressure are inferred for various locations on the cylinder. Some features of the three‐dimensional resultant pressure field are also discussed.
Subject Classification: 20.30.
58(1975); http://dx.doi.org/10.1121/1.380675View Description Hide Description
The purpose of this paper is to demonstrate that at small values of the Mach number a harmonically rich radiated field will result from the simple harmonic (sinusoidal) motion of an oscillating body when the amplitude of oscillation is large. An asymptotic solution of the equations of inviscid compressible flow is obtained which is valid in the small Mach number limit. To a given order of approximation, the effects of fluid nonlinearity (nonlinearity in the equations of motion and the equation of state) do not enter, and the harmonic distortion is due entirely to large‐amplitude boundary motion. In higher approximations, where both the effects of boundary motion and fluid nonlinearity enter, the former effect can still control the amplitude of certain harmonics of the radiated acoustic field. The results are obtained by the method of matched asymptotic expansions, which is ideally suited for the purpose of distinguishing the harmonic distortion due to large displacements from that due to fluid nonlinearity. The method is used to make the connection between the field far from the source, and the nonpropagating hydrodynamic flow field near the oscillating body.
Subject Classification: 25.55; 20.15, 20.60.
58(1975); http://dx.doi.org/10.1121/1.380676View Description Hide Description
According to ray acousticssonic boom is limited to a ’’corridor’’ on the ground by atmospheric refraction. Beyond the edge of the corridor on either side lies a region void of incident or reflected rays—the ’’shadow zone’’—the treatment of which is beyond the scope of ray acoustics. In this paper, a technique is developed for extending the prediction of the sonic boom signature into the shadow zone using diffraction theory. The calculations indicate that the portion of this region lying along the horizontal plane boundary behaves like a low‐pass acoustic filter. This has the effect of progressively rounding and attenuating the sonic boom signature as the shadow zone is penetrated—an observable characteristic of experimental records. In a separate calculation, an empirical variable reflection factor based on the angle of incidence of the shock wave in the sound field is obtained to correct the bell‐shaped 3/4‐power curve of amplitude variation across the corridor.
Subject Classification: 28.55 28.40; 20.30. 20.20.
Investigation of the amplitude fluctuations of high‐frequency short‐duration.sound pulses propagated under short‐range shallow‐water conditions58(1975); http://dx.doi.org/10.1121/1.380677View Description Hide Description
This paper reports on part of a general investigation that has been carried out to determine the feasibility and limits of performance of high‐data‐rate underwater digital data communication. Specifically, the paper deals with the amplitude fluctuations that are encountered when high‐frequency 0.8‐msec duration pulses are transmitted under short‐range shallow‐water conditions. In the paper, the results of an analysis of experimentally measured amplitude fluctuations are presented. The results, which are presented in the form of amplitude‐frequency spectra, autocorrelation functions, and probability density functions, are interpreted in terms of the prevailing climatic conditions, and the results are related to existing relevant theories of fluctuations.
Subject Classification: 30.20.
Comparison of sonar system performance achievable using synthetic‐aperture techniques with the performance achievable by more conventional means58(1975); http://dx.doi.org/10.1121/1.380678View Description Hide Description
A comparison is made of the signal‐to‐noise characteristics of synthetic‐aperture sonar and conventional sonar. For the synthetic‐aperture sonar case a design procedure is described which makes possible the choice of essentially any unambiguous range and any resolution. Often multiple beam receivers are required. It is shown for the synthetic‐aperture sonar case that the horizontal aperture is the major factor affecting area coverage rate. The comparisons are made with as many parameter values as spossible identical for both the synthetic‐aperture cases and the nonsynthetic‐aperture cases. If identical physical aperture dimensions are used and other parameters held to identical values, the synthetic‐aperture sonar gives higher signal‐to‐ratio than does the nonsynthetic‐aperture sonar primarily because the latter must operate at higher acoustic frequencies for which signal attenuation becomes extremely large. If the sonar systems are operated at the same frequency, then the nonsynthetic aperture sonar can give a higher signal‐to‐noise ratio only when its physical aperture is larger than that used in the synthetic‐aperture case.
Subject Classification: 30.82; 60.20.
58(1975); http://dx.doi.org/10.1121/1.380679View Description Hide Description
A perturbation procedure is applied, through the second order of approximation, to the three‐dimensional problem of scattering of sound from a point source by a rough surface progressing in the wind direction over an isovelocity ocean. The results satisfy conservation of energy, in a ray‐theoretic sense, and are uniformly valid throughout the field. At points in the region of surface‐image interference (Lloyd’s‐mirror region), the signal is shown to be strongly modulated. Results are presented which depict the power in the carrier and signal sidebands. The latter are not, in general, symmetric in amplitude about the carrier. However, it is demonstrated analytically that, on two specific planes in the field, the signal power spectrum is symmetric about the carrier.
Subject Classification: 30.40, 30.20, 30.25.
58(1975); http://dx.doi.org/10.1121/1.380680View Description Hide Description
The specular reflection and transmission of an acoustic plane wave at a randomly rough two‐fluid interface is studied. The perturbation method of Bass is used to derive a new set of boundary conditions to replace the unperturbed boundary conditions. The new conditions are valid for surfaces characterized by arbitrary anisotropiccorrelation functions. Using these new boundary conditions, reflection and transmission coefficients are derived. It is shown that in the Kirchhoff approximation, the reflection and transmission coefficients reduce to those obtained earlier by Eckhart, Clay, Medwin, and Hagy. In the limit of the density of one of the fluids going to zero, the reflection coefficient for a rough pressure release surface is obtained. Results are presented using ocean surface models in terms of wind speed and direction.
Subject Classification: 30.40, 30.30, 30.25,30.20.
58(1975); http://dx.doi.org/10.1121/1.380671View Description Hide Description
This paper describes the design, fabrication, and use of both passive and active electrical dummy loads which simulate the electrical impedance of an individual transducer element in a large array over a wide range of frequencies. These impedance characteristics allow the use of this dummy load for the testing of a prototype amplifier at both its operating frequencies and frequencies where the stability and noise performance of the amplifier may be affected by the impedance characteristics of the load. Since an active port is included in this dummy load, the impedance characteristics of a transducer element at various positions in the array could readily be simulated. An example of the use of this dummy load for the testing of a 1‐kW switching type prototype amplifier is given.
Subject Classification: 30.85; 85.40, 85.64.
Acoustic phase fluctuations resulting from axis meander and transport variation of a geostrophic ocean current58(1975); http://dx.doi.org/10.1121/1.380672View Description Hide Description
A treatment is presented of total‐field phase fluctuations of a cw signal, transmitted across a slowly varying northward geostrophic flow. Only refracted/bottom‐reflected rays are considered, and the ocean bottom is horizontal. Unlike earlier investigations, the flow is of finite width and transport‐axis location, as well as volume transport, may be varied. We begin with a rather general current model having factorable dependence on depth and distance across the flow. The current is taken to decrease linearly with depth, and the surface current is specialized to a cubic polynomial.Sound speed is calculated from the density and pressure solutions. It is then approximated by a linear least‐squares fit, so that the acoustics problem is equivalent to that in a convergent channel with linear sound speed versus depth. In an application, the total‐field phase is shown to be highly sensitive to transport‐axis meander as well as to changes in volume transport.
Subject Classification: 30.20, 30.25.
58(1975); http://dx.doi.org/10.1121/1.380681View Description Hide Description
The model of the standard linear solid is extended to the viscoelasticanisotropic medium by defining a relaxation‐time tensor. The velocity and attenuation of sound waves are calculated as a function of frequency from the components of this tensor and low‐ and high‐frequency elastic constants. The anisotropic behavior of relaxation curves can be described in this formalism.
Subject Classification: 35.50.
58(1975); http://dx.doi.org/10.1121/1.380682View Description Hide Description
The experimental work of the Eaton–Peabody Laboratory of Auditory Physiology requires chambers unusually free of ambient acoustic, vibratory, and electric noise, so that small mechanical or electric signals in response to low‐level sounds can be measured. This paper deals with the problems that arose in setting of criteria, the design, and the construction of such chambers, and reports on the evaluation of their performance. The ambient acoustic noise is well below the human threshold of hearing even with the ventilation system operating. The noise reduction between the control rooms and the chambers is almost 80 dB at 250 Hz and more than 90 dB above 500 Hz. The octave‐band ambient vibration acceleration level at the experimental tables in the chambers is below −120 dB r e lg.
Subject Classification: 55.40; 65.10.
58(1975); http://dx.doi.org/10.1121/1.380683View Description Hide Description
Consideration of a proposed electrical model of monaural detection leads to the suggestion that subjects listening to long‐duration signals may respond on the basis of amplitude peaks. To eliminate such peaks, a 500‐Hz tone was employed as both masker and signal. A two‐interval, forced‐choice procedure was used to determine the level required for 80% correct at each of several signal durations. The masker level was 60 dB SPL, and the signal was always in phase with the masker. Signal durations from 20 msec to 2 sec were employed. The results showed a slope of approximately −3 dB per doubling over the range from 20 msec to 1 sec. Detection at 2 sec tended to be worse than at 1 sec. The slope of 03 dB per doubling is steeper than has commonly been found with noise maskers, especially at the longer durations. The psychometric function exhibites a systematic change of slope with duration—steep for short durations and shallow for long.
Subject Classification: 65.35, 65.58, 65.75.
58(1975); http://dx.doi.org/10.1121/1.380684View Description Hide Description
Three observers tried to detect a 500‐Hz target in white noise in one of two temporal intervals. A distractor tone was added to the target interval on half of the trials and to the nontarget interval on the remainder. When the distractor was within about 40 Hz of 500 Hz, the 80% correct threshold for the target was elevated or depressed depending on whether the distractor was added to the nontarget or target interval. Thus, the critical band around 500 Hz is estimated to be about 80 Hz wide. It is possible to compare the relative sizes of the two threshold shifts against the predictions of two models of detection: the classical, integrated‐energy model, and a model emphasizing contrast among the energy of the components within the band. To make these predictions, simulated observers were run under the identical procedure. Within the limits of experimental error, the simulation matched the data well only under the integrated‐energy model. Under that model, the observers are performing about 2. to 3 dB worse than what the simulation predicts, which provides an estimate of the internal noise as nearly equal to the external noise.
Subject Classification: 65.58, 65.75; 50.70.
58(1975); http://dx.doi.org/10.1121/1.380685View Description Hide Description
Old World monkeys (Macaca) were trained to vocalize at a steady rate in the laboratory by the use of operant conditioning techniques with food as a reinforcer. While the animals were vocalizing, they were subjected to one of two noise bands (200–500 Hz or 8–16 kHz) at different sound pressure levels (70, 80, and 90 dB SPL). Vocal amplitude was measured as a function of the SPL of the noise bands. The monkeys increased voice amplitude to the band of low‐frequency noise but not to the high‐frequency band. These results suggest that in monkey, as in man, a relation exists between speaking and hearing: both man and monkey will increase voice amplitude in the presence of masking noise of the appropriate spectral composition.
Subject Classification: 65.22; 70.20.
58(1975); http://dx.doi.org/10.1121/1.380686View Description Hide Description
Four chinchillas were trained to respond differently to sustained ‖a‖ and ‖i‖. The ensemble of vowels included two repetitions of each of the vowels by each of four talkers at each of three pitch levels for a total of 24 ‖a‖’s and 24 ‖i‖’s. The sound levels of the vowels were randomly changed from trial to trial over a 10‐dB range. The animals easily transferred the training to a new set of vowels produced by 24 new talkers. Subsequently, the animals similarly transferred to synthetic ‖a‖’s and ‖i‖’s. The only relevant difference between the synthetic vowels was their formant structure, while there were irrelevant differences in their pitch contours. We conclude that the chinchilla can abstract some essential difference(s) between sustained ‖a‖ and ‖i‖ and ignore irrelevant variations of sound level, pitch level, pitch contour, and voice quality. These results are discussed in terms of perceptual learning and auditory concept formation.
Subject Classification: 70.30; 65.75; 80.50.
58(1975); http://dx.doi.org/10.1121/1.380687View Description Hide Description
Spectrographic data are presented which suggest that it may be possible to estimate the frequency of the fundamental resonance of the cavity behind the mouth opening, the ’’front cavity resonance,’’ from information in the speech signal. It is shown that place of articulation information in the steady states, transitions, and bursts of F 2 (or sometimes F 3) can be reinterpreted to be information from the front cavity resonance. Furthermore, a number of synthesis results that have appeared anomalous when described in terms of numbered formants seem to find a coherent explanation in terms of the front cavity resonance. Implications for theories of speech perception include the possibility that an estimate of front cavity resonance frequency may serve for continuous articulatory reference.
Subject Classification: 70.20, 70.30.
58(1975); http://dx.doi.org/10.1121/1.380688View Description Hide Description
This is a summary report of the vowel duration data that have been accumulated over the past several years. The data corpus analyzed to derive temporal controls of vowels consists mainly of three different readings by three different speakers, each about 10 to 20 min in duration. The rules cover the temporal behavior of vowels under many phonological conditions. The conditions include stressed and unstressed positions, prepausal and nonprepausal positions, word‐final and non‐word‐final conditions, and monosyllabic and polysyllabic words. The influence of following consonants is discussed as well. Included also are conditions other than phonological ones, such as the effect of the prominence of words on their vowels, and the speed of reading. The duration rules derived from the data are intended for use in our speech synthesis‐by‐rule system from printed text.
Subject Classification: 70.20, 70.70.
58(1975); http://dx.doi.org/10.1121/1.380689View Description Hide Description
Acoustical transmission lines formed into a spiral configuration possess the latent property of having different lengths along adjacent lines when traversing along a radius: for an acoustical spiral, sound waves in adjacent transmission lines will progress from an antiphase relation at the center of the spiral to an in‐phase relation at some radius r (λ) from the center. This is a transformation dependent only upon wavelength. When those transmission ‐ line walls that are facing the environment are covered with a low‐mass, tightly stretched membrane, radiation from this secondary surface will occur at the appropriate time. Radiation of a transverse wave rotating about the spiral axis occurs when sound waves in adjacent transmission lines are in phase. In this paper, several radiation modes and phasing properties are discussed. Owing to automatic adjustment of aperture size with change in frequency, the spiral membrane enclosure has a broad and constant beamwidth. An acoustical source, such as a loudspeaker cone each side of which is contiguous to the end of an acoustical transmission line, generates within those transmission lines longitudinal waves that are antiphase relative to each other. Constant loading of the source occurs over a wide range of frequencies, providing uniform electrical/acoustical performance. An experrimental model is described.
Subject Classification: 85.60; 20.40.
58(1975); http://dx.doi.org/10.1121/1.380690View Description Hide Description
Among different methods, the transmission‐line or the impedance tube method has been most popular for the experimental evaluation of the acoustical impedance of any termination. The current state of method involves extrapolation of the measured data to the reflecting surface or exact locations of the pressure maxima, both of which are known to be rather tricky. The present paper discusses a method which makes use of the positions of the pressure minima and the values of the standing‐wave ratio at these points. Lippert’s concept of enveloping curves has been extended. The use of Smith or Beranek charts, with their inherent inaccuracy, has been altogether avoided. The existing formulas for the impedance have been corrected. Incidentally, certain other errors in the current literature have also been brought to light.
Subject Classification: 85.20.